The increasing sophistication of semiconductor technology has resulted in a significant shift away from aluminum as the dominant metal in multi-level metallization processes. As semiconductor chip manufacturing has moved from AlCu/SiO2 based interconnect technology to Cu/Low k ILD (low dielectric constant interlayer dielectrics) technology, several integration issues such as delamination, peeling, and cracking have become apparent. Accordingly, these issues have evidenced a need for accurate measurement and control of the mechanical strength of the dielectric layers.
Nano-indentation and bending tests have been the commonly used methods to determine the elastic moduli of both opaque and transparent materials. With nano-indentation, a load is applied to an indenter to force it into a material. As the indenter is forced into the material, the amount that the indenter is displaced into the material is measured. Concurrently with the measurement of the indenter displacement, the load applied to the indenter is measured. However, when forcing an indenter into a thin film, not only will the thin film deform, but the substrate will deform as well. Bending tests apply strain to measure failure characteristics of a material.
When applied to thin films, these methods fail to accurately describe behavior as the scale of thin films is reduced to micron and sub-micron dimensions. Because both nano-indentation and bending tests are destructive, are contact based in nature, and have large errors and very low throughput, they are not suitable for semiconductor process control. Another disadvantage of these methods is that they require larger test areas than the area that the typical process design rules allow.
As can be appreciated, a non-destructive, non-contact, small spot, high throughput and high accuracy method is needed that is compatible with semiconductor production throughput requirements, and for accurate measurement and control of the elastic moduli of the dielectric films used in the semiconductor industry.